There is also a detent mechanism to lock it in the open position
While theres a lot of synergy here, the cards are mostly strong independently, and the deck is designed to play a fair, interactive game that just happens to be able to gain infinite life with Urza and the Thopter Foundry / Sword of the Meek Combo, but mostly Urza, Oko, and Emry are all amazing standalone cards that require fairly different answers
Fell Stinger Deploy the Fell Stinger with its deathly scorpion's sting, and you can exploit (sacrifice another creature,) to evoke its 2 cards for 2 life ability, which can target any player
The reason why Blossoming Tortoise is so high on this list, however, is that its likely to appear in Pioneer extensively at least for a period of time
That means if someone casts a ten-mana spell, they are going to be milling ten cards on their next untap step